Dual-ovenable, heat-sealable packaging film

ABSTRACT

A dual ovenable film having a first layer comprising one or more polyamides and a second layer comprising one or more polyamides. The first layer forms the first outer surface of the film. The second layer has a melting point of at least about 210° C. The film is capable of forming a water-containing package by providing two 4 inch by 6 inch sheets of the film each having four perimeter sides, placing the sheets in superimposed, coextensive arrangement having the first layers of the films in contact with each other, and heat sealing three perimeter sides of the sheets together using a ⅛-inch wide sealing bar at a temperature of 290° F., a dwell time of 0.5 seconds, and a sealing pressure of 40 psig to form an open pouch having heat seals along three of the four perimeter sides. The open pouch can be filled with 100 milliliters of distilled water at a temperature of 73° F and the fourth perimeter side of the sheet can be heat sealed together under the same conditions as used to seal the three perimeter sides to form a closed package having a heat seal along the fourth perimeter side and containing the water. The seal strength of the resulting heat seals is at least 1 pound/inch after the closed, water-containing package has been exposed to three hours in a conventional oven at 400° F. (air temperature). The film may be used to form heat sealed pouches at “polyolefin-type” of heat seal conditions, yet the integrity of the heat seals may be maintained even when the heat seal is exposed to conventional oven conditions.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to multilayer packaging films, forexample, useful in applications requiring a high degree of dimensionalstability at elevated oven temperatures, and more particularly todual-ovenable, heat-sealable packaging films.

[0002] For the convenience of consumers, packaged food may be designedto be placed directly in a microwave or conventional oven to heat orcook the food without first removing the packaging. The consumer thusavoids having to handle the raw product or to clean a container in whichthe food would have otherwise been placed for cooking or heating. Theconsumer may also simply dispose of the packaging material after heatingor cooking the food.

[0003] Packaging that can withstand exposure to the heating and/orcooking environment of a selected type of oven is said to be “ovenable”with respect to that type of oven. To be ovenable with respect to amicrowave oven, the packaging should not, for example, include materialssuch as metals that reflect microwaves to cause arcing or otherwisedamage the oven's microwave generation. To be ovenable with respect to aconventional oven, the packaging should, for example, be able in use towithstand exposure to 400° F. air temperature for up to four hours.Packaging that is ovenable both with respect to a microwave oven and aconventional oven is said to be “dual-ovenable.”

[0004] Food packaging may be formed by heat sealing thermoplastic filmto itself to form a pouch or similar article containing the food. Thisheat sealing operation typically occurs at the food packager's plantusing a heat sealing machine designed for high speed operation. Althoughthere are several variations, generally a heat sealing machine includesa heated seal bar that contacts and compresses the two films to be heatsealed together. Three variables are important in forming a heatseal: 1) the seal bar temperature, 2) the dwell time, and 3) the sealingpressure. The seal bar temperature is the surface temperature of theseal bar. The dwell time is the length of time that the heated seal barcontacts the film to transfer heat from the seal bar to soften at leasta portion of the films (e.g., the sealing layers of the films) so thatthey may be melded together. The sealing pressure is the amount of forcethat squeezes the films together during this heat transfer. All of thesevariables interact in completing a successful heat seal.

[0005] Because the heat sealing layers for much of the thermoplasticpackaging films used in food packaging are based on relativelylow-melting polyolefin thermoplastics (or similar melt-temperaturethermoplastics), the heat sealing machines present in food packagingplants are often designed and set to operate with a seal bartemperature, a dwell time, and a sealing pressure in a range useful forsuch materials. This permits the heat sealing machines to operate athigh speeds to form strong seals. Such a heat sealing machine mayoperate at, for example, a seal bar temperature of 290° F., a dwell timeof 0.5 seconds, and a sealing pressure of 40 psig.

[0006] An existing ovenable packaging material for conventional ovens isa monolayer film based on a blend of nylon 6 with nylon 6,6. However,this film requires a relatively high sealing temperature to effect auseful heat seal. For example, at a sealing pressure of 40 psig and adwell time of 0.5 seconds, the sealing bar temperature is generally atleast about 380° F. Because typical existing heat sealing machines infood packaging plants cannot easily accommodate operation at thoseconditions, rather than forming a heat seal, a metal clip is typicallyused to close food-packaging based on this film, in which case theresulting food packaging is not dual ovenable. Further, a metal clip isan expensive closure method compared to heat sealing—and limits the useof X-ray examination to check packages for metallic contaminants.

[0007] The addition of a heat seal layer of relatively low-meltingpolyolefin thermoplastic to the existing monolayer film of a blend ofnylon 6 and nylon-6,6 would result in a two-layer film that is heatsealable at the “polyolefin-type” of heat sealing conditions discussedabove; however, such a film would not be able to form heat seals thatare ovenable in conventional ovens because the relatively low-meltingpolyolefin layer would melt, decompose, or delaminate from the nylonlayer upon exposure to a 400° F. conventional oven for three hours.

SUMMARY OF THE INVENTION

[0008] The present invention addresses one or more of the aforementionedproblems. A film comprises a first layer comprising one or morepolyamides and a second layer comprising one or more polyamides. Thesecond layer has a melting point of at least about 210° C. The firstlayer forms the first outer surface of the film.

[0009] The film is capable of forming a water-containing package byproviding two 4 inch by 6 inch sheets of the film each having fourperimeter sides, placing the sheets in superimposed, coextensivearrangement having the first layers of the films in contact with eachother, and heat sealing three perimeter sides of the sheets togetherusing a ⅛-inch wide sealing bar at a temperature of 290° F., a dwelltime of 0.5 seconds, and a sealing pressure of 40 psig to form an openpouch having heat seals along three of the four perimeter sides. Theopen pouch can be filled with 100 milliliters of distilled water at atemperature of 73° F. and the fourth perimeter side of the sheet can beheat sealed together under the same conditions as used to seal the threeperimeter sides to form a closed package having a heat seal along thefourth perimeter side and containing the water. The seal strength of theresulting heat seals is at least 1 pound/inch after the closed,water-containing package has been exposed to three hours in aconventional oven at 400° F. (air temperature).

[0010] It was unexpected that the integrity of a heat seal formed by afilm at “polyolefin-type” of heat seal conditions would be maintainedwhere the heat seal was exposed to conventional oven conditions.

[0011] These and other objects, advantages, and features of theinvention will be more readily understood and appreciated by referenceto the detailed description of the invention and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a representational cross-section of a two-layer film ofthe present invention;

[0013]FIG. 2 is a representational cross-section of a film of thepresent invention having at least three layers;

[0014]FIG. 3 is a representational cross-section of another film of thepresent invention having at least three layers;

[0015]FIG. 4 is a representational cross-section of a film of thepresent invention having at least four layers;

[0016]FIG. 5 is a perspective view of a pouch comprising the film of thepresent invention; and

[0017]FIG. 6 is a perspective view of a container comprising the film ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The film of the present invention includes at least two layers:first layer 12 and second layer 14. For two-layer film 10 (FIG. 1),first layer 12 forms the first outer surface 16 of the film and secondlayer 14 forms the second outer surface 18 of film 10 opposite outersurface 16. For a film comprising three or more layers, both the firstand second layers 12, 14 may be outer layers forming the outsidesurfaces of the film 20 (FIG. 2) with one or more additional layers 22between the first and second layers—or the second layer 14 may form aninterior layer of film as shown by film 30 (FIG. 3) with one or moreadditional layers 24 oriented to the exterior of second layer 14. For afilm comprising four or more layers, the second layer 14 may form aninterior layer of film as shown by film 40 (FIG. 4) with one or moreadditional layers 22 between the first and second layers and with one ormore additional layers 24 oriented to the exterior of second layer 14.

[0019] The film of the present invention may comprise, for example, atleast 3 layers, at least 4 layers, at least 5 layers, from 2 to 4layers, from 2 to 5 layers, and from 5 to 9 layers. As used herein, theterm “layer” refers to a discrete film component which is coextensivewith the film and has a substantially uniform composition. Where two ormore adjacent layers have essentially the same composition, then thesetwo or more adjacent layers may be considered a single layer for thepurposes of this application.

[0020] The film 10 (or any film of the present invention) may be formedinto a bag or pouch 50 (FIG. 5), for example, one suitable for packaginga food product. In forming such a bag, the first layer 12 may be sealedto itself to form the heat seal seams 52 of the bag. In this manner, thefirst layer 12 (i.e., the “heat seal layer” or “sealant layer”) of thefilm is considered the “inside” or food-side layer of the film and thebag made from the film. The “outside layer” of the film may be secondlayer 14 (as shown in FIG. 1) or the outside layer may formed by one ofthe one or more layers 24 (as shown in FIG. 4).

First Layer of the Film

[0021] The first layer 12 facilitates heat sealing the film to itself orto another object, such as a support member or tray, and accordingly maybe considered the sealant layer.

[0022] The sealant layer comprises one or more polyamides. Usefulpolyamides may include those of the type that may be formed by thepolycondensation of one or more diamines with one or more diacids and/orof the type that may be formed by the polycondensation of one or moreamino acids. Useful polyamides include aliphatic polyamides andaliphatic/aromatic polyamides.

[0023] Representative aliphatic diamines for making polyamides includethose having the formula:

H₂N(CH₂)_(n)NH₂

[0024] where n has an integer value of 1 to 16. Representative examplesinclude trimethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, octamethylenediamine,decamethylenediamine, dodecamethylenediamine, hexadecamethylenediamine.Representative aromatic diamines include p-phenylenediamine,4,4′-diaminodiphenyl ether, 4,4′ diaminodiphenyl sulphone,4,4′-diaminodiphenylethane. Representative alkylated diamines include2,2-dimethylpentamethylenediamine, 2,2,4-trimethylhexamethylenediamine,and 2,4,4 trimethylpentamethylenediamine. Representative cycloaliphaticdiamines include diaminodicyclohexylmethane. Other useful diaminesinclude heptamethylenediamine, nonamethylenediamine, and the like.

[0025] Representative diacids for making polyamides include dicarboxylicacids, which may be represented by the general formula:

HOOC—Z—COOH

[0026] where Z is representative of a divalent aliphatic radicalcontaining at least 2 carbon atoms. Representative examples includeadipic acid, sebacic acid, octadecanedioic acid, pimelic acid, subericacid, azelaic acid, dodecanedioic acid, and glutaric acid. Thedicarboxylic acids may be aliphatic acids, or aromatic acids such asisophthalic acid and terephthalic acid.

[0027] The polycondensation reaction product of one or more or the abovediamines with one or more of the above diacids may form usefulpolyamides. Representative polyamides of the type that may be formed bythe polycondensation of one or more diamines with one or more diacidsinclude aliphatic polyamides such as poly(hexamethylene adipamide)(“nylon-6,6”), poly(hexamethylene sebacamide) (“nylon-6,10”),poly(heptamethylene pimelamide) (“nylon-7,7”), poly(octamethylenesuberamide) (“nylon-8,8”), poly(hexamethylene azelamide) (“nylon-6,9”),poly(nonamethylene azelamide) (“nylon-9,9”), poly(decamethyleneazelamide) (“nylon-10,9”), poly(tetramethylenediamine-co-oxalic acid)(“nylon-4,2”), the polyamide of n-dodecanedioic acid andhexamethylenediamine (“nylon-6,12”), the polyamide ofdodecamethylenediamine and n-dodecanedioic acid (“nylon-12,12”).

[0028] Representative aliphatic/aromatic polyamides includepoly(tetramethylenediamine-co-isophthalic acid) (“nylon-4,I”),polyhexamethylene isophthalamide (“nylon-6,I”), poly (2,2,2-trimethylhexamethylene terephthalamide), poly(m-xylylene adipamide)(“nylon-MXD,6”), poly(p-xylylene adipamide), poly(hexamethyleneterephthalamide), poly(dodecamethylene terephthalamide), andpolyamide-MXD,I.

[0029] Representative polyamides of the type that may be formed by thepolycondensation of one or more amino acids include poly(4-aminobutyricacid) (“nylon-4”), poly(6-aminohexanoic acid) (“nylon-6” or“poly(caprolactam)”), poly(7-aminoheptanoic acid) (“nylon-7”),poly(8-aminooctanoic acid) (“nylon-8”), poly(9-aminononanoic acid)(“nylon-9”), poly(10-aminodecanoic acid) (“nylon-10”),poly(11-aminoundecanoic acid) (“nylon-11”), and poly(12-aminododecanoicacid) (“nylon-12”).

[0030] Representative copolyamides include copolymers based on acombination of the monomers used to make any of the foregoingpolyamides, such as, nylon-4/6, nylon-6/6, nylon-6/9,caprolactam/hexamethylene adipamide copolymer (“nylon-6,6/6”),hexamethylene adipamide/caprolactam copolymer (“nylon-6/6,6”),trimethylene adipamide/hexamethylene azelaiamide copolymer(“nylon-trimethyl 6,2/6,2”), hexamethyleneadipamide-hexamethylene-azelaiamide caprolactam copolymer(“nylon-6,6/6,9/6”), hexamethyleneadipamide/hexamethylene-isophthalamide (“nylon-6,6/6,I”), hexamethyleneadipamide/hexamethyleneterephthalamide (“nylon-6,6/6,T”), nylon-6,T/6,I,nylon-6/MXD,T/MXD,I, nylon-6,6/6, 10, and nylon-6,I/6,T.

[0031] Conventional nomenclature typically lists the major constituentof a copolymer before the slash (“/”) in the name of a copolymer;however, in this application the constituent listed before the slash isnot necessarily the major constituent unless specifically identified assuch. For example, unless the application specifically notes to thecontrary, “nylon-6/6,6” and “nylon-6,6/6” may be considered as referringto the same type of copolyamide.

[0032] Polyamide copolymers may include the most prevalent polymer unitin the copolymer (e.g., hexamethylene adipamide as a polymer unit in thecopolymer nylon-6,6/6) in mole percentages ranging from any of thefollowing: at least about 50%, at least about 60%, at least about 70%,at least about 80%, and at least about 90%, and the ranges between anyof the forgoing values (e.g., from about 60 to about 80%); and mayinclude the second most prevalent polymer unit in the copolymer (e.g.,caprolactam as a polymer unit in the copolymer nylon-6,6/6) in molepercentages ranging from any of the following: less than about 50%, lessthan about 40%, less than about 30%, less than about 20%, less thanabout 10%, and the ranges between any of the forgoing values (e.g., fromabout 20 to about 40%).

[0033] Useful polyamides include those that are approved by thecontrolling regulating agency (e.g., the U.S. Food and Drug Agency) foreither direct contact with food and/or for use in a food packaging film,at the desired conditions of use.

[0034] The sealant layer may comprise one or more polyamides in anamount of any of the following ranges based on the weight of the sealantlayer: at least about 70%, at least about 80%, at least about 90%, atleast about 95%, at least about 96%, and at least about 98%. Further,the sealant layer may comprise about 100% polyamide, may consist of oneor more polyamides, or may consist essentially of one or morepolyamides.

[0035] The sealant layer may comprise more than one polyamide such as ablend of polyamides, for example, two polyamides, at least twopolyamides, three polyamides, and at least three polyamides. The sealantlayer may comprise a first polyamide in any of the following amounts(based on the weight of the sealant layer): at least about 40%, at leastabout 50%, at least about 60%, at least about 70%, at least about 80%,at least about 90%, at least about 95%, and the ranges between any ofthese forgoing values (e.g., from about 60 to about 80%).

[0036] The sealant layer may comprise a second polyamide in any of thefollowing amounts (based on the weight of the sealant layer): less thanabout 60%, less than about 50%, less than about 40%, less than about30%, less than about 20%, less than about 10%, and less than about 5%,and the ranges between any of these forgoing values (e.g., from about 20to about 40%).

[0037] The sealant layer may comprise a third polyamide in any of thefollowing amounts (based on the weight of the sealant layer): less thanabout 60%, less than about 50%, less than about 40%, less than about30%, less than about 20%, less than about 10%, and less than about 5%,and the ranges between any of these forgoing values (e.g., from about 20to about 40%).

[0038] Each of the first, second, and third polyamides of the sealantlayer may be selected from any of the polyamides described above, forexample, nylon-6, nylon-6,6, nylon-6,12, nylon-6,6/6,10, andnylon-6,I/6,T. The sealant layer may comprise at least one of nylon-6and nylon-6,6. The sealant layer may comprise, for example, any of thefollowing combinations: nylon-6 and nylon-6,6/6,10; nylon-6 andnylon-6,1/6,T; nylon-6,6 and nylon-6,12; nylon-6, nylon-6,6/6,10, andnylon-6,I/6,T; and nylon-6, nylon-6,12, and nylon-6,I/6,T.

[0039] To facilitate heat sealing at polyolefin-type sealing conditions(as discussed in the Background section) the sealant layer 12 may have asoftening characteristic such that two representative samples of thefilm that are heat sealed together (with the sealant layers of the filmsfacing each other)—using a ⅛-inch wide sealing bar at a temperatureselected from 290° F. and 300° F., a dwell time of 0.5 seconds, and asealing pressure of 40 psig—forms a heat seal having a seal strength (asdiscussed below) of at least about any of the following: 1 pound/inch, 2pound/inch, 2.5 pound/inch, and 3 pounds/inch.

[0040] The sealant layer may have a melting point less than about any ofthe following values: 220° C., 210° C., 200° C., 190° C., and 180° C.;and the melting point of the sealant layer may be at least about any ofthe following values: 120° C., 130° C., 140° C., and 150° C. Allreferences to the melting point of a polymer, a resin, or a film layerin this application refer to the melting peak temperature of thedominant melting phase of the polymer, resin, or layer as determined bydifferential scanning calorimetry according to ASTM D-3418.

[0041] If the sealant layer comprises amorphous material, then thesealing layer may not clearly display a melting point. The glasstransition temperature for the sealing layer may be less than about, andmay range between about, any of the following values: 125° C., 120° C.,110° C., 100° C., 90° C., 80° C., 70° C., 60° C., and 50° C.; measuredwhere the relative humidity may be any of the following values: 100%,75%, 50%, 25%, and 0%. All references to the glass transitiontemperature of a polymer, a resin, or a film layer in this applicationrefer to the characteristic temperature at which glassy or amorphouspolymers become flexible as determined by differential scanningcalorimetry (DSC) according to ASTM D-3417.

[0042] The sealant layer may comprise a polyamide blend comprising oneor more relatively high-melting point polyamides with one or morerelatively low-melting point polyamides. The sealant layer may comprisesuch a polyamide blend in at least about any of the following amountsbased on the weight of the sealant layer: 70%, 80%, 90%, and 95%. Therelatively high-melting point polyamides may have a melting point of atleast about any of the following values: 210° C., 215° C., 220° C., 225°C., 230° C., 235° C., 240° C., 245° C., 250° C., 255° C., 260° C., 265°C., 270° C., 275° C., 280° C., 285° C., 290° C., 295° C., and 300° C.;and may range between any of the forgoing values (e.g., from about 235to about 280° C.). Representative relatively high-melting pointpolyamides may include nylon-6, nylon-6,6, nylon-6/6,6, nylon-6,10,nylon-6,12, nylon-6/6,T, nylon-MXD,6, nylon-4,6, nylon-6,9, andnylon-6,6/6,10 (having less than about 10% or more than about 60%nylon-6,6 in the copolymer).

[0043] The relatively low-melting point polyamides may have a meltingpoint of less than about any of the following values: 210° C., 205° C.,200° C., 195° C., 190° C., 185° C., and 180° C. Representativerelatively low-melting point polyamides may include nylon-6/12,nylon-12, nylon-12,T, nylon-6/6,9, nylon-11, and nylon-6,6,/6,10 (havingfrom about 10% to about 60% nylon-6,6 in the copolymer).

[0044] The amount of relatively high-melting point polyamide in thepolyamide blend of relatively high-melting point polyamide withrelatively low-melting point polyamide may be at least about, may beless than about, and may range between about any of the followingamounts (based on the weight of the blend): 1%, 5%, 10%, 10%, 20%, 30%,40%, and 50%. The amount of relatively low-melting point polyamide inthe blend of relatively high-melting point polyamide with relativelylow-melting point polyamide may be at least about, may be less thanabout, and may range between about any of the following amounts (basedon the weight of the blend): 50%, 60%, 70%, 80%, 90%, 95%, and 99%.

[0045] The sealant layer may comprise a polyamide blend comprising afirst relatively high-melting point polyamide with a second relativelyhigh-melting point polyamide. The sealant layer may comprise such apolyamide blend in at least about any of the following amounts based onthe weight of the sealant layer: 70%, 80%, and 90%.

[0046] The sealant layer may comprise a blend of two or more polyamideswhere each polyamide of the blend has a melting point higher than themelting point of the blend, for example, where the melting point rangefor the blend includes any of the melting point ranges as set forth forthe sealant layer above.

[0047] The sealant layer may comprise one or more amorphous polyamides,for example, nylon-6,I/6,T. The sealant layer may comprise amorphouspolyamide in an amount at least about, at most about, and rangingbetween about any of the following values (based on the weight of thesealant layer): 20%, 30%, 40%, 50%, 60%, 70%, and 80%.

[0048] The thickness of sealant layer 12 is selected to providesufficient material to effect a strong heat seal bond, yet not so thickso as to negatively affect the ovenable characteristics of the film toan unacceptable level. The sealant layer may have a thickness of atleast about any of the following values: 0.05 mils, 0.1 mils, 0.15 mils,0.2 mils, 0.25 mils, 0.3 mils, 0.35 mils, 0.4 mils, 0.45 mils, 0.5 mils,and 0.6 mils. The sealant layer may have a thickness less than about anyof the following values: 5 mils, 4 mils, 3 mils, 2 mils, 1 mil, 0.7mils, 0.5 mils, and 0.3 mils. The thickness of the sealant layer as apercentage of the total thickness of the film may be less that about anyof the following values: 50%, 40%, 30%, 25%, 20%, 15%, 10%, and 5%; andmay range between any of the forgoing values (e.g., from about 10% toabout 30%).

Second Layer of the Film

[0049] The second layer 14 may comprise one or more polyamides such asany of those discussed above in any of the following amounts based onthe weight of the second layer: at least about 70%, at least about 80%,at least about 90%, at least about 95%, at least about 96%, and at leastabout 98%. Further, the second layer may comprise about 100% polyamide,may consist of one or more polyamides, or may consist essentially of oneor more polyamides.

[0050] The second layer may comprise more than one polyamide such as ablend of polyamides, for example, two polyamides, at least twopolyamides, three polyamides, and at least three polyamides. The secondlayer may comprise a first polyamide of at least about, and betweenabout, any of the following amounts (based on the weight of the secondlayer): 60%, 70%, 80%, and 90%. The second layer may comprise a secondpolyamide of less than about, and between about, any of the followingamounts (based on the weight of the second layer): 50%, 40%, 30%, 20%,and 10%.

[0051] Each of the first and second polyamides of the second layer maybe selected from, for example, nylon-6, nylon-6,6, nylon-6/6,6,nylon-6,10, nylon-6,12, nylon-6,6/6,10, nylon-6/6,T, nylon-MXD,6, andnylon-4,6. The second layer may comprise any of nylon-6, nylon-6,6, andnylon-6/6,6, and combinations thereof, such as both nylon-6 andnylon-6,6.

[0052] The second layer may comprise one or more amorphous polyamides,for example, nylon-6,I/6,T. The second layer may comprise amorphouspolyamide in an amount at least about, at most about, and rangingbetween about any of the following values (based on the weight of thesecond layer): 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80%.

[0053] To enhance the high-temperature performance of the film, thesecond layer 14 may have a melting point of at least about any of thefollowing values: 210° C., 220° C., 230° C., 240° C., 250° C., 260° C.,270° C., 280° C., 290° C., and 300° C.; and may range between any ofthese forgoing values.

[0054] The glass transition temperature for the second layer may be lessthan about, and may range between, any of the following values: 125° C.,120° C., 110° C., 100° C., 90° C., 80° C., 70° C., 60° C., and 50° C.;measured where the relative humidity may be any of the following values:100%, 75%, 50%, 25%, and 0%.

[0055] The second layer may have a melting point greater than themelting point of the sealant layer by at least about any of thefollowing values: 20° C., 30° C., 40° C., 50° C., 60° C., 70° C., 80°C., 90° C., and 100° C.

[0056] The second layer may comprise a polyamide blend comprising two ormore relatively high-melting point polyamides, such as those discussedabove with respect to the sealant layer.

[0057] The amount of relatively high-melting point polyamide in thepolyamide blend of the second layer may be at least about, and may rangebetween, any of the following amounts (based on the weight of theblend): 70%, 80%, 90%, 95%, 100%.

[0058] The thickness of second layer 14 may be selected to providesufficient material to enhance the ovenable characteristics of the film.The second layer may have a thickness of at least about any of thefollowing values: 0.5 mils, 0.75 mils, 1 mil, 2 mils, 3 mils, 4 mils.The second layer may have a thickness less than about any of thefollowing values: 10 mils, 6 mils, 5 mils, 4 mils, and 3 mils. Thethickness of the second layer as a percentage of the total thickness ofthe film may be at least about any of the following values: 40%, 50%,60%, 70%, 80%, and 90%; and may range between any of the forgoing values(e.g., from about 40% to about 90%).

Other Layers of the Film

[0059] The film of the present invention may include one or moreadditional layers 22, 24. The additional layers may comprise any of thematerials, and in any of the amounts, discussed above with respect tothe first and second layers.

[0060] The additional layers 22, 24 may comprise one or more barriercomponents. Useful barrier components include: ethylene/vinyl alcoholcopolymer (“EVOH”), polyacrylonitrile (“PAN”), and polyamide, forexample, nylon-MXD,6 (either with or without nanocomposite),nylon-MXD,6/MXD,I.

[0061] EVOH may have an ethylene content of, for example, between about20% and 45%, between about 25% and 35%, and 32% by weight. EVOH mayinclude saponified or hydrolyzed ethylene/vinyl acetate copolymers, suchas those having a degree of hydrolysis of at least 50%, preferably of atleast 85%. EVOH may be a retortable grade EVOH, such as those availablefrom Nippon Goshei.

[0062] The additional layer comprising a barrier component may have athickness and composition sufficient to impart to the film incorporatingthe barrier layer an oxygen transmission rate of no more than about anyof the following values: 150, 100, 50, 45, 40, 35, 30, 25, 20, 15, 10,and 5 cubic centimeters (at standard temperature and pressure) persquare meter per day per 1 atmosphere of oxygen pressure differentialmeasured at 0% relative humidity and 23° C. All references to oxygentransmission rate in this application are measured at these conditionsaccording to ASTM D-3985.

[0063] An additional layer may comprise barrier component in an amountof at least about any of the following: 50%, 60%, 70%, 80%, 90%, and100%, based on the weight of the additional layer comprising the barriercomponent. The thickness of an additional layer may be any of thefollowing: from about 0.05 to about 6 mils, from about 0.05 to about 4mils, from about 0.1 to about 3 mils, and from about 0.12 to 2 mils.

Additives

[0064] Either or both of the layers 12 and 14—or any of the polyamideresins or blends—may comprise effective amounts of one or morenucleating agents. Effective amounts and types of nucleating agents areknown to those of skill in the art.

[0065] Either or both of the layers 12 and 14—or any of the polyamideresins or blends—may comprise effective amounts of one or morenanocomposite clay materials. Effective amounts and types ofnanocomposite agents are known to those of skill in the art.

[0066] Either or both of the layers 12 and 14—or any of the polyamideresins or blends—may comprise effective amounts of one or more heatstabilizers. Effective amounts and types of heat stabilizers are knownto those of skill in the art, and include, for example, those availableunder the the Solutia NA-189 trademark and the Honeywell MB-HStrademark. The layer may comprise at least about any of the followingamounts of heat stabilizer: 0.2%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 2%, 2.5%,3%, 4%, and 5%, and may range between any of those values (e.g., fromabout 0.5% to about 3%).

[0067] One of more of the layers 12, 14, 22, 24 may include one or moreadditives useful in packaging films, such as, antiblocking agents, slipagents, antifog agents, colorants, pigments, dyes, flavorants,antimicrobial agents, meat preservatives, antioxidants, fillers,radiation stabilizers, and antistatic agents. Such additives, and theireffective amounts, are known in the art.

The Film

[0068] The film 10, 20, 30, 40 may be capable of forming heat sealsunder “polyolefin-type” heat seal conditions where the heat seals have aseal strength that can withstand the expected conditions of use inmicrowave and conventional ovens. To determine whether a film has such acapability, for example, a water-containing package is formed byproviding two 4 inch by 6 inch sheets of the film. The sheets are placedin superimposed, coextensive arrangement having the first layers of thefilms in contact with each other. Three perimeter sides of the sheetsare heat sealed together using a ⅛-inch wide sealing bar at a specifiedtemperature selected from 290° F. and 300° F., a dwell time of 0.5seconds, and a sealing pressure of 40 psig to form an open pouch havingheat seals along three of the four perimeter sides. The pouch is filledwith 100 milliliters of distilled water at a temperature of 73° F. Thefourth perimeter sides of the sheets are heat sealed together under thesame conditions as used to seal the three perimeter sides. The resultingclosed pouch has a heat seal along the fourth perimeter side andcontains the water.

[0069] The closed, water-containing pouch is exposed to an amount oftime selected from three or four hours in a conventional oven at 400° F.(air temperature). After removal from the oven and cooling to roomtemperature, representative samples are cut from the pouch to measurethe seal strength of the heat seals. The resulting seal strength of theheat seals may be at least about any of the following values: 1, 1.5, 2,2.5, 3, 3.5, 4, 4.5, 5, 6, and 10 pounds/inch. The term “seal strengthof a heat seal” (or similar terms) as used herein means the maximumamount of force (pounds/inch) required to separate or delaminate twofilms that have been heat sealed together, as measured in accordancewith ASTM F88-94 where the Instron tensile tester crosshead speed is 5inches per second, using five, 1-inch wide, representative samples.

[0070] Haze is a measurement of the transmitted light scattered morethan 2.5° from the axis of the incident light. Haze is measured againstthe outside surface 16 or 18 of the film (FIGS. 1 to 4), according tothe method of ASTM D 1003, which is incorporated herein in its entiretyby reference. All references to “haze” values in this application are bythis standard. The haze of the film may be no more than about any of thefollowing values: 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, and 1%. Thefilm may have any of these haze values after a representative sample ofthe film is placed for two hours in a conventional oven having an airtemperature of 400° F.

[0071] The film of the present invention may be transparent (at least inthe non-printed regions) so that the packaged article is visible throughthe film. “Transparent” as used herein means that the material transmitsincident light with negligible scattering and little absorption,enabling objects (e.g., packaged food or print) to be seen clearlythrough the material under typical unaided viewing conditions (i.e., theexpected use conditions of the material). The transparency (i.e.,clarity) of the film may be at least about any of the following values:20%, 25%, 30%, 40%, 50%, 65%, 70%, 75%, 80%, 85%, and 95%, as measuredin accordance with ASTM D1746. All references to “transparency” valuesin this application are by this standard.

[0072] The transparency and the haze of the film may be measured beforeand after the film has been formed into a closed, water-containingpouch, as discussed above, and after the package has been exposed in aconventional oven at 400° F. (air temperature) for an amount of timeselected from 3 hours and 4 hours. After removal from the oven andcooling to room temperature, representative samples may be taken fromthe pouch. The transparency and haze of the film before and after thisexposure may remain substantially the same—for example, the transparencymay not have decreased by more than 5% points (e.g., from a 95%transparency to a 90% transparency) and the haze may not have increasedby more than 5% points (e.g., from 10% haze to 15% haze).

[0073] The film of the present invention may comprise one or morepolyamides in an amount of any of the following ranges based on theweight of the film: at least about 70%, at least about 80%, at leastabout 90%, at least about 95%, at least about 96%, and at least about98%. Further, the film may comprise about 100% polyamide, may consist ofone or more polyamides, or may consist essentially of one or morepolyamides.

[0074] The film of the present invention may comprise less than aboutany of the following amounts of polyolefin (based on the weight of thefilm): 20%, 15%, 10%, 5%, 3%, 2%, and 1%; and the amount of polyolefinin the film may range between any two of these values (e.g., from about2% to about 15%). The film may be substantially free of polyolefin.

[0075] The film of the present invention may comprise less than aboutany of the following amounts of polyester (based on the weight of thefilm): 20%, 15%, 10%, 5%, 3%, 2%, and 1%; and the amount of polyester inthe film may range between any two of these values (e.g., from about 2%to about 15%). The film may be substantially free of polyester.

[0076] The film of the present invention may have a heat-shrinkableattribute. For example, the film may have a free shrink in at least onedirection (i.e., machine or transverse direction), in at least each oftwo directions (machine and transverse directions), or a total freeshrink measured at 220° F. of at least about any of the following: 3%,7%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 55%, 60%, and 65%. Further, thefilm may have any of a free shrink in at least one direction (machine ortransverse direction), in at least each of two directions (machine andtransverse directions), or a total free shrink of at least about any ofthese listed shrink values when measured at any of 100° F., 120° F.,140° F., 160° F., 185° F., 190° F., 200° F., and 210° F.

[0077] As is known in the art, the total free shrink is determined bysumming the percent free shrink in the machine (longitudinal) directionwith the percentage of free shrink in the transverse direction. Forexample, a film which exhibits 50% free shrink in the transversedirection and 40% free shrink in the machine direction has a total freeshrink of 90%. Although preferred, it is not required that the film haveshrinkage in both directions. Unless otherwise indicated, each referenceto free shrink in this application means a free shrink determined bymeasuring the percent dimensional change in a 10 cm×10 cm specimen whensubjected to selected heat (i.e., at a certain temperature exposure)according to ASTM D 2732.

Manufacture of the Film

[0078] The film of the present invention may be manufactured bythermoplastic film-forming processes known in the art (e.g., tubular orblown-film extrusion, coextrusion, extrusion coating, flat or cast filmextrusion). A combination of these processes may also be employed.

[0079] The film may be oriented or non-oriented. The film may beoriented in either the machine (i.e., longitudinal) or the transversedirection, or in both directions (i.e., biaxially oriented), forexample, in order to enhance the optics, strength, and durability of thefilm. For example, the film may be oriented in one of the machine ortransverse directions or in both of these directions by at least aboutany of the following ratios: 2:1, 2.5:1, 2.7:1, 3:1, 3.5:1, and 4:1. Thefilm may be oriented in one of the machine or transverse directions orin both of these directions by no more than about any of the followingratios: 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, and 4:1. If the film is oriented,then it may be heat set or annealed after orientation to reduce the heatshrink attribute to a desired level or to help obtain a desiredcrystalline state of the film.

Use of the Film

[0080] The film may be used in packaging an article or object, forexample, packaging food, where the food packaging may be exposed tomicrowave or conventional oven conditions or both (i.e., dual ovenable)to heat or cook the food. Such food may comprise for example, fresh,raw, partially-cooked, or cooked food, such as red meat products (e.g.,beef, veal, lamb, and pork), poultry, and pre-prepared products such aspizza and pasta.

[0081] To form the packaged article, the film of the present inventionmay be heat sealed to either another film or to itself (for example, bya fin seal and/or a lap seal arrangement) to form an open package suchas a bag, pouch (e.g., vertical or horizontal form-fill-sealed pouch),tube, or other containment configuration in which the article to bepackaged is placed before the package is sealed closed.

[0082] The film 10 (or any of the films of the present invention) may beheat sealed to a support member 62 (FIG. 6), such as a thermoformed trayhaving a central depressed area 68 and a surrounding peripheral flange64. The food product 66 may first be placed on the tray. The film 10 maythen be positioned over the food and heat sealed to the peripheralflange 64 of the tray to hermetically enclose the food product and formcontainer 70 enclosing food 66. In such arrangement, the film 10 is the“lid” or “lidstock” and the tray 62 is a “support member.”

[0083] Heat sealing may occur by one or more of thermal conductance heatsealing, impulse sealing, ultrasonic sealing, and dielectric sealing.

[0084] Any of the above-described food may be enclosed in a packagecomprising the film of the present invention, e.g., a pouch made of thefilm, as described above. The food may then be heated, reheated, orcooked by placing the food enclosed in the package in an oven andactivating the oven to heat or cook the food enclosed in the package toa desired level.

[0085] The following examples are presented for the purpose of furtherillustrating and explaining the present invention and are not to betaken as limiting in any regard. Unless otherwise indicated, all partsand percentages are by weight.

[0086] In the following examples these abbreviations may be used:

[0087] “PA1-6” is a nylon-6 having a melting point of 220° C. availablefrom BASF Corporation (Parsippany, N.J.) under the Ultramid B4trademark.

[0088] “PA2-6 and -6,6” is a blend of nylon-6 and nylon-6,6 believed toinclude about 50 to 55 weight % nylon-6 and about 45 to 50 weight %nylon-6,6 available from Honeywell Corporation under the Capron 2120 FNtrademark.

[0089] “PA3-6” is a nylon-6 having a melting point of 220° C. availablefrom Honeywell Corporation under the Capron B205 trademark.

[0090] “PA1-6N” is a nylon-6 with 1% nucleating agent having a meltingpoint of 220° C. available from BASF Corporation (Parsippany, N.J.)under the Ultramid KR4418 trademark.

[0091] “PA1-6,6” is a nylon-6,6 having a melting point of 264° C.available from Solutia Corporation (Pensacola, Fla.) and supplied byPrime Alliance (Des Moines, Iowa) under the ASCEND 66J trademark.

[0092] “PA2-6,6” is a nylon-6,6 having a melting point of 264° C.available from BASF Corporation under the Ultramid A4 trademark.

[0093] “PA1-6/12” is a nylon-6/12 having a melting point of 130° C.available from EMS Corporation (Sumter, S.C.) under the Grilon CF6Strademark.

[0094] “PA1-6,6/6” is a nylon-6,6/6 copolymer having a melting point of217° C. available from Solutia Corporation (Pensacola, Fla.) andsupplied by Prime Alliance (Des Moines, Iowa) under the Ascend 76HFtrademark.

[0095] “PA1-6,6/6,10” is a nylon-6,6/6,10 having a melting point of 200°C. available from EMS Corporation (Sumter, S.C.) under the GrilonBM20SBG trademark.

[0096] “PA1-6,I/6,T” is an amorphous nylon-6,I/6,T copolymer having adry glass transition temperature of 125° C. available from DupontCorporation (Wilmington, Del.) under the Selar 2072 trademark.

[0097] “PA1-MXD,6” is a nylon-MXD,6 having a melting point of 243° C.available from Mitsubishi Corporation under the Nylon MXD6-6007tradename.

[0098] “PA2-MXD,6” is a nylon-MXD,6 including nanocomposite availablefrom Nanocor Corporation (Arlington Heights, Ill.) under the Imperm N37tradename.

[0099] “HS” is a heat stabilizer masterbatch available from SolutiaCorporation (Pensacola, Fla.) and supplied by Prime Alliance (DesMoines, Iowa) under the NA-189 trade name.

[0100] “EVOH” is a retortable grade ethylene/vinyl alcohol having amelting point of 183° C. and an ethylene content of 32 mole % availablefrom Nippon Goshei (via Soarus of Arlington Heights, Ill.) under thetradename Soamol SG372B.

EXAMPLES 1-10

[0101] The examples 1-10 shown in Table 1 below were made by a cast filmextrusion process. TABLE 1 Thickness PA1- PA2-6 PA1- PA1- PA1- PA1- PA1-Layer (mil) 6 and -6,6 6,6 6/12 6,6/6,10 6,6/6 6,I/6,T EVOH Ex 1 1st0.25 80% 20% 2^(nd) 0.875 100% 3rd 0.875 100% Ex 2 1st 0.25 40% 60%2^(nd) 0.875 100% 3rd 0.875 100% Ex 3 1st 0.25 20% 80% 2^(nd) 0.875 100%3rd 0.875 100% Ex 4 1st 0.25 25% 75% 2^(nd) 1.75 100% Ex 5 1st 0.25 30%70% 2^(nd) 1.75 100% Ex 6 1st 0.25 25% 75% 2^(nd) 1.75 40% 60% Ex 7 1st0.25 30% 70% 2^(nd) 1.75 40% 60% Ex 8 1st 0.25 25% 75% 2^(nd) 0.875 100%3rd 0.875 40% 60% Ex 9 1st 0.25 25% 75% 2^(nd) 0.875 100% 3rd 0.875 40%60% Ex 10 1st 0.25 25% 75% 2^(nd) 0.875 100% 3rd 0.875 100%

EXAMPLES 11-20

[0102] The Examples 11-24 shown in Table 2 below were made by a blownfilm extrusion process. TABLE 2 PA1- PA2- Thick- PA1- PA3- PA1- PA1-PA2- PA1- PA1- MXD, MXD, ness 6 6 6N 6,6 6,6 6,6/6,10 6,I/6,T 6 6 HSEVOH Layer (mil) (wt %) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) Ex1^(st) 0.25 24 75 1 11 2^(nd) 1.5 40 60 3^(rd) 0.25 24 75 1 Ex 1^(st)0.25 30 69 1 12 2^(nd) 0.875 40 60 3^(rd) 0.875 30 69 1 Ex 1^(st) 0.5620 59 20 1 13 2^(nd) 1.41 70 30 Ex 1^(st) 0.56 20 59 20 1 14 2^(nd) 1.4140 60 Ex 1^(st) 0.47 20 59 20 1 15 2^(nd) 1.43 40 60 Ex 1^(st) 0.62 2059 20 1 16 2^(nd) 0.45 69.3 30 0.7 3^(rd) 0.29 100 4^(th) 0.72 69.3 300.7 Ex 1^(st) 0.50 20 59 20 1 17 2^(nd) 1.40 40 60 Ex 1^(st) 0.40 20 5920 1 18 2^(nd) 0.50 39.6 60 0.4 3^(rd) 0.35 100 4^(th) 0.50 39.6 60 0.4Ex 1^(st) 0.50 20 59 20 1 19 2^(nd) 0.50 39.6 60 0.4 3^(rd) 0.25 1004^(th) 0.50 39.6 60 0.4 Ex 1^(st) 0.50 20 59 20 1 20 2^(nd) 0.50 39.6 600.4 3^(rd) 0.50 100 4^(th) 0.50 39.6 60 0.4 Ex 1^(st) 0.5 20 59 20 1 212^(nd) 1.5 39 60 1 Ex 1^(st) 0.58 20 59 20 1 22 2^(nd) 0.53 39.6 60 0.43^(rd) 0.27 100 4^(th) 0.98 39.6 60 0.4 Ex 1^(st) 0.5 24 75 1 23 2^(nd)1.5 40 60 Ex 1^(st) 0.5 20 59 20 1 24 2^(nd) 1.5 69.3 30 0.7

[0103] The example 16 film had a haze of 11.6%, a transmittance of93.6%, and a clarity of 29.08%. The Example 23 film had a haze of26.03%, a transmittance of 93.8%, and a clarity of 1.00%. The Example 24film had a haze of 13.65%, a transmittance of 93.6%, and a clarity of35.43%. Transmittance is measured according to the method of ASTM D1003. All references to “transmittance” values in this application areby this standard.

[0104] A heat seal was formed (or was attempted to be formed) for eachof the following films shown in Table 3 by placing the heat seal layerof a sheet of the subject film in contact with the heat seal layer ofanother sheet of the same film. The superimposed sheets were exposed to80 psig sealing pressure for a 1 second dwell time using a Sencorp Model12ALS/1 sealer at the seal bar temperature shown below. The strength ofthe resulting heat seal is shown in Table 3. TABLE 3 Seal Bar TempExample 21 Example 19 (° F.) Seal Strength (lbf/in) Seal Strength(lbf/in) 266 0.298 0.367 284 2.52 7.49 302 6.83 9.4 320 6.2 8.47

[0105] A heat seal was formed (or was attempted to be formed) for eachof the following films shown in Table 4 by placing the heat seal layerof a sheet of the subject film in contact with the heat seal layer ofanother sheet of the same film. The superimposed sheets were exposed to40 psig sealing pressure for a 0.5 second dwell time using a SencorpModel 12ALS/1 sealer at the seal bar temperature shown below. Thestrength of the resulting heat seal is shown in Table 4. Comp 1(comparative 1) is a 1.2 mil mono-layer nylon film commerciallyavailable from Gem Polymer Corporation as Crystal 33. Comp 2(comparative 2) is a 0.79 mil mono-layer film of nylon-6 and nylon-6,6blend commercially available from Reynolds Corporation under theReynolds Oven Bag trade name. TABLE 4 Example Example Example 21 19 13Comp 1 Comp 2 Seal Bar Seal Strength Seal Strength Seal Strength SeatStrength Seal Strength Temp (° F.) (lbf/in) (lbf/in) (lbf/in) (lbf/in)(lbf/in) 257 0.135 0.128 0.152 266 0.227 0.207 0.264 275 0.447 0.6543.14 284 2.66 2.16 5.15 293 5.24 4.9 6.47 302 7.23 7.39 7.17 320 6.937.25 8.03 338 8.78 9.61 9.41 0.439 0.0754 356 2.38 0.0549 374 4.1 0.131392 2.15

Cooking Example

[0106] The film of Example 16 was used to form three 12 inch by 18 inchpouches each having three edges heat sealed together using an impulsesealer to seal the edge areas of the first layers of the superimposedsheets together. Raw meat was placed into each pouch through its openfourth edge. A 0.5 pound pork tenderloin was placed into the firstpouch; and a three pound chicken was placed into each of the second andthird pouches. The fourth edge of each pouch was then vacuum heat sealedusing a Koch vacuum sealing machine to form three closed packagesenclosing the meat.

[0107] The first closed pouch was then placed in a microwave oven andcooked on high power for 5 minutes. The first pouch puffed up duringcooking. The second closed pouch was placed in the microwave oven andcooked on high power for 20 minutes. The second pouch puffed up duringthe cooking process and the chicken enclosed in the second pouch becamefully cooked and browned on top. The Example 16 film from which thefirst and second pouches were formed remained clear and flexible. Theintegrity of the heat seals of each of the first and second pouches weremaintained during the microwave oven cooking exposure.

[0108] The third closed pouch was placed in a convection oven set at177° C. (350° F.) for 2 hours. The third pouch puffed up during thecooking process and the chicken became fully cooked and browned on top.The Example 16 film from which the third pouch was formed remained clearand flexible. The integrity of the heat seals of the third closed pouchwere maintained during the convection oven cooking exposure.

[0109] The above descriptions are those of preferred embodiments of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as defined in theclaims, which are to be interpreted in accordance with the principles ofpatent law, including the doctrine of equivalents. Except in the claimsand the specific examples, or where otherwise expressly indicated, allnumerical quantities in this description indicating amounts of material,reaction conditions, use conditions, molecular weights, and/or number ofcarbon atoms, and the like, are to be understood as modified by the word“about” in describing the broadest scope of the invention. Any referenceto an item in the disclosure or to an element in the claim in thesingular using the articles “a,” “an,” “the,” or “said” is not to beconstrued as limiting the item or element to the singular unlessexpressly so stated. All references to ASTM tests are to the mostrecent, currently approved, and published version of the ASTM testidentified, as of the priority filing date of this application. Eachsuch published ASTM test method is incorporated herein in its entiretyby this reference.

What is claimed is:
 1. A film comprising: a first layer comprising oneor more polyamides; and a second layer comprising one or morepolyamides, wherein the second layer has a melting point of at leastabout 210° C.; wherein: the film has first and second opposite outersurfaces and the first layer forms the first outer surface of the film;and the film is capable of forming a water-containing package byproviding two 4 inch by 6 inch sheets of the film each having fourperimeter sides, placing the sheets in superimposed, coextensivearrangement having the first layers of the films in contact with eachother, heat sealing three perimeter sides of the sheets together using a⅛-inch wide sealing bar at a temperature of 290° F., a dwell time of 0.5seconds, and a sealing pressure of 40 psig to form an open pouch havingheat seals along three of the four perimeter sides, filling the openpouch with 100 milliliters of distilled water at a temperature of 73°F., heat sealing the fourth perimeter sides of the sheets together underthe same conditions as used to seal the three perimeter sides to form aclosed package having a heat seal along the fourth perimeter side andcontaining the water, where the seal strength of the heat seals is atleast 1 pound/inch after the closed, water-containing package has beenexposed to three hours in a conventional oven at 400° F. (airtemperature).
 2. The film of claim 1 wherein the sealing bar has atemperature of 300° F.
 3. The film of claim 1 wherein the first layerhas a melting point and the melting point of the second layer is atleast about 20° F. greater than the melting point of the first layer. 4.The film of claim 1 wherein the first layer comprises at least twopolyamides.
 5. The film of claim 1 wherein the first layer has a glasstransition temperature of less than about 120° C. measured at a 50%relative humidity.
 6. The film of claim 1 wherein the first layercomprises at least 70% by weight of the first layer of a blendcomprising one or more polyamides having a melting point of at leastabout 210° C. and one or more polyamides having a melting point of lessthan about 210° C.
 7. The film of claim 6 wherein the blend comprises atleast about 50% by weight of the blend of the one or more polyamideshaving a melting point of less than about 210° C.
 8. The film of claim 1wherein the first layer comprises at least 20% amorphous polyamide byweight of the first layer.
 9. The film of claim 1 wherein the firstlayer comprises at least about 80% of one or more polyamides by weightof the first layer.
 10. The film of claim 1 wherein the first layercomprises less than about 50% of the total thickness of the film. 11.The film of claim 1 wherein the first layer comprises two or morepolyamides selected from nylon-6, nylon-6,6, nylon-6,6/6,10, nylon-6,12,and nylon-6,I/6,T.
 12. The film of claim 1 wherein the first layercomprises nylon-6, nylon-6,6/6,10, and nylon-6,I/6,T.
 13. The film ofclaim 1 wherein the second layer comprises at least about 50% of thetotal thickness of the film.
 14. The film of claim 1 wherein the secondlayer comprises at least about 80% of one or more polyamides by weightof the second layer.
 15. The film of claim 1 wherein the second layercomprises one or more polyamides selected from nylon-6, nylon-6,6, andnylon-6/6,6.
 16. The film of claim 1 wherein the second layer forms thesecond outer surface of the film.
 17. The film of claim 1 wherein thefilm is capable of forming a heat seal having a seal strength of atleast about 4 lbf-in where the heat seal is formed by heat sealing thefirst layers of two sheets of the film together using a ⅛-inch widesealing bar at a temperature of 300° F., a dwell time of 0.5 seconds,and a sealing pressure of 40 psig.
 18. The film of claim 1 wherein thehaze of the film after two hours of exposure to air temperature of 400°F. in a conventional oven is less than about 20%.
 19. The film of claim1 wherein the first layer comprises one or more heat stabilizers. 20.The film of claim 1 wherein the film comprises less than about 20% ofpolyolefin by weight of the film.
 21. The film of claim 1 wherein thefilm is substantially free of polyolefin.
 22. The film of claim 1wherein the film comprises less than about 20% polyester by weight ofthe film.
 23. The film of claim 1 wherein the film is substantially freeof polyester.
 24. A packaged food comprising: a food; and a packageenclosing the food, wherein the package comprises the film of claim 1.25. The film of claim 1 wherein the film comprises a third layercomprising ethylene/vinyl alcohol.
 26. The film of claim 1 wherein thefirst layer consists essentially of one or more polyamides.
 27. The filmof claim 1 wherein the melting point of the first layer is less thanabout 220° C.
 28. The film of claim 1 wherein the film has an oxygentransmission rate of no more than about 150 cubic centimeters (atstandard temperature and pressure) per square meter per day per 1atmosphere of oxygen pressure differential measured at 0% relativehumidity and 23° C.
 29. The film of claim 1 wherein the film comprisesat least about 70 weight % polyamide by weight of the film.
 30. A methodof heating a food comprising: providing a food enclosed in a packagecomprising the film of claim 1; placing the food enclosed in the packagein an oven; and activating the oven to heat the food enclosed in thepackage to a desired level.